This invention relates to the field of decoupling capacitors for integrated circuits. More particularly, this invention relates to novel and improved decoupling capacitors, and methods of formation thereof wherein the capacitors are formed in a two step molding process to form decoupling capacitors which are auto-insertable into printed circuit boards for use in conjunction with dual-in-line integrated circuits or other electronic components.
U.S. patent application Ser. No. 403,408 (which is assigned to the assignee hereof, and the entire contents of which are incorporated herein by reference) discloses a decoupling capacitor for an integrated circuit package. The decoupling capacitor of that prior application is a thin rectangular chip of ceramic material which is metallized on opposite sides and has leads from the metallized coatings on opposite sides of the chip at two points adjacent a pair of diagonally opposed corners of the rectangularly shaped ceramic chip. The two leads are bent downwardly, and the decoupling capacitor assembly is encapsulated in a film of nonconductive material. In accordance with the teachings of that prior application, the decoupling capacitor is dimensioned so as to be received in the space between the two rows of leads extending from a conventional dual-in-line integrated circuit. The two leads from the decoupling capacitor are plugged into a printed circuit board, with these leads from the capacitor being inserted into the printed circuit through holes to which the ground power supply conductors are connected. The associated integrated circuit or other electronic component is then positioned over the capacitor and inserted into the board such that the power supply leads of the integrated circuit or other component will be positioned in the same through holes of the printed circuit board in which the two capacitor leads have been inserted.
The diagonally located leads or pins on the decoupling capacitor of application Ser. No. 403,408 have resulted in a problem when it is desired to automatically insert the decoupling capacitors into the printed circuit board. Standard auto-insertion equipment is available for inserting integrated circuit elements into the printed circuit boards. The insertion heads on standard auto-insertion equipment grasp the integrated circuit about the bent terminal pins or leads of the integrated circuit. Since there are two symmetric rows of pins on the integrated circuit element, the auto-insertion equipment can grasp the integrated circuit element symmetrically and stably for insertion. However, when insertion of the decoupling capacitor of prior application Ser. No. 403,408 is attempted with the same auto-insertion equipment, an unstable condition and misalignment results because of the fact that the decoupling capacitor, rather than having two symmetrical rows of pins, has only two pins at diagonally opposite corners of the rectangular capacitor. Because of the presence of only the two pins, the capacitor "cocks" in the insertion head with the result that misalignment occurs between the terminals of the capacitor in the corresponding holes on the printed circuit board.
Since it is extremely desirable to auto-insert the decoupling capacitors into the printed circuit boards, and since it is equally desirable to perform that auto-insertion with the same auto-insertion equipment used with the integrated circuit elements, a significant problem is encountered with the decoupling capacitor of the prior application, not from the standpoint of its electronic operability and effectiveness, but rather from the standpoint of adapting it to high volume assembly techniques.
A need also exists for a decoupling capacitor structure which is both auto-insertable, hermetically sealed, and capable of being manufactured by automated assembly processes.
U.S. patent application Ser. No. 456,654 (assigned to the assignee hereof) discloses one approach to solving the above discussed auto-insertion problem by the incorporation of dummy or stabilizing pins in a decoupling capacitor assembly. U.S. patent application Ser. No. 551,466 Watson for "Decoupling Capacitor and Method of Manufacture Thereof" and U.S. patent application Ser. No. 552,107 for "Decoupling Capacitor and Method of Manufacture Thereof" of David S. Fishman, both of which are being filed simultaneously herewith and are assigned to the assignee hereof present other constructions of and methods for forming decoupling capacitors with dummy pins or molded stabilizing lugs. The present invention presents other constructions of and methods for forming improved decoupling capacitors which are hermetically sealed, auto-insertable and manufactured in an automated two step molding process.
One problem in many of the prior art configurations is related to the size constraints imposed on the decoupling capacitor system by the intended end use of the capacitor beneath an IC on a printed circuit board. These capacitors typically include a ceramic capacitor chip (a ceramic body with opposed conductive face surfaces), a pair of conductive plates abutting the face surface of the chip with an active pin extending from each plate, and an insulating outer covering or case. In particular, the thickness or height dimension is limited to about 0.038 to 0.040 inch. Since the ceramic capacitor chip is about 0.009 to 0.010 inch thick and each conductive plate is about 0.007 inch thick, only about 0.007 to 0.0085 inch per side remains available for encapsulation or other covering by an insulated casing. Because of manufacturing tolerances, the insulating cover may be breached, thus leading to problems of contamination, short circuiting, etc.